The invention relates to the establishing of calls in a telecommunication network comprising dual or multi mode terminals, for instance DECT/GSM terminals that can be used like cordless terminals in a private network exchange and like a cellular dual mode terminal in a cellular mobile telephone network. Within the scope of the present application terminals of that description are called dual mode terminals (DMT) and the users correspondingly DMT subscribers.
Cordless telephone systems--like DECT (Digital European Cordless Telephone), which is described in recommendation 300 175 of ETSI--support subscriber mobility in a very limited fashion. Within the scope of the present application, such a network is called a network supporting limited subscriber mobility.
Mobile telephone networks, like the European GSM/DCS system, well support subscriber mobility outdoors. Within the scope of the present application, such a network is called a network supporting extensive subscriber mobility. Cordless PABX:s support subscriber mobility in areas that are typically limited to indoor spaces. Furthermore, the PABX provides the subscriber with exchange services.
Dual or multi mode terminals DMT are developed with a view to subscriber mobility both indoors and outdoors. Such a DMT terminal requires new qualities of the mobile telephone network, e.g. for numbering, mobility management and call routing of the DMT subscriber. Known mobile networks cannot handle subscriber mobility in a system comprising both networks that support limited subscriber mobility and networks that support extensive subscriber mobility.